NR-I (nitrogen regulator I), the product of the g1nG gene or Escherichia coli, is required for the transcription of a set of genes activated when growth is limited by the source of nitrogen in the medium. The first operon induced by nitrogen-limited growth is the glnALG operon, which codes for glutamine synthetase, an essential enzyme for ammonia assimilation. Activation of glnApw, the major promoter of the operon, is greatly stimulated by the binding of NR-I to sites on the DNA which can be moved to positions far upstream or downstream from the start site of transcription and still activate normally. Furthermore, NR-I must be phosphorylated by the product of the glnL gene before it can activate transcription. These features of regulation have not been previously described in prokaryotes, but are common features of the control of transciption in eukaryotes: enhancers and protein kinases have been implicated in the inappropriate expression of genes in transformed or cancerous cells. It is the purpose of this study to use the power of genetics in E. coli to determine details of the mechanism by which NR-I activates transcription. The methods to be used are largely genetic and should allow determination of 1) which amino acids are involved in the contacts of NR-I with DNA, 2) whether binding of NR-I are required for transcription, and 4) how phosphorylation might activate NR-I. It might also be possible to determine which amino acids of NR-I contact RNA polymerase: there is virtually nothing known about how activators interact with RNA polymerase.